The present invention relates to a procedure and device for changing an endless felt.
The invention is designed especially for the changing of the upper felt in the press of a chemical-pulp drying machine, which is mainly the context in which it will be described in the following, but it can just as well be applied in the changing of other felts in chemical-pulp, paper or cardboard machines.
Traditionally, the presses in chemical-pulp drying machines are of a cantilevered type, and a felt change is performed by removing the spacers on the press roller and/or operating side of the frame and supporting the press roller by means of cantilever girders from the driving side to produce a gap into which the felt can be inserted. After this, the endless felt is spread out on the floor on the operating side, from where it is then lifted onto the press using suitable lifting apparatus while at the same time its lower part is being red into the gap thus opened. Once the felt has been passed into position and straightened, the spacers are mounted again and the felt is tightened in position.
However, there are several drawbacks in prior-art technology. In a cantilevered machine, changing the felt is a difficult and slow operation that takes several hours. When the felt is spread out on the floor on the operating side and when it is being installed in the machine, it becomes soiled with dirt and grease and it is also creased, so it is not immediately usable after installation but has to be cleaned, which further prolongs the down-time. Moreover, press felts currently used are thicker and heavier than before, so they are difficult to handle and pass between the rollers. Likewise, there is a high risk of the felts being damaged during installation as they get creased and bent.
A further drawback in cantilevered presses currently used is that the cantilever system requires a heavy structure, long beams and a large space on the driving side, in addition to the structural engineering requirements relating to the machine room floor.
The object of the present invention is to eliminate the drawbacks mentioned above. A specific object of the present invention is to disclose a new type of procedure and a corresponding device which allow a simpler and faster felt change operation and which also permit a substantially simpler and cheaper structure of the machine in which the felt is used.
In the procedure of the invention for changing an endless felt, the felt is placed around the rollers by raising a first roller and passing the felt around the first roller as well as the other rollers to go inside the felt loop. According to the invention, the endless felt is placed around an elongated lifting beam and the lifting beam is attached to the first end of the first roller. Next, the fixtures attaching the first end of the first roller to the frame are released, whereupon the first end of the roller can be raised, supported by the lifting beam. The felt around the lifting beam can now be passed under the raised first roller and around the first roller and the other rollers to go inside the felt loop, whereupon the first roller is lowered and secured in place. After this, the lifting beam can be released from the first roller.
Preferably before the new felt is passed into position, the rollers to go inside the felt are moved closer to each other to facilitate installation of the felt. Correspondingly, after the felt has been installed, at is tightened in position by moving the rollers inside the felt farther apart from each other.
The procedure can be applied to change the felts in the press of a chemical pulp, paper or cardboard machine, preferably upper felts, in which case the first roller is the upper roller of the press.
In the procedure of the invention, only as much of the endless felt loop is unwound from the roll as is needed to allow it to be placed around a lifting beam while the rest of the felt remains rolled up, supported by the lifting beam. Thus, it is not necessary to spread the entire felt on the floor, where it would get soiled and creased. This is also an easier way to handle the felt.
In the procedure of the invention, only a portion of the felt is unwound from the roll at first and the entire felt is continuously kept straight in its whole width, and it need not be creased or bent in any way in its widthways direction.
The device of the invention for changing an endless felt comprises an elongated lifting beam around which a partially unwound endless felt can be passed. The first end of the lifting beam comprises fixing elements for attaching it to the first end of the first roller. Similarly, the first end of the first roller is provided with counter elements corresponding to the fixing elements, allowing the lifting beam and the first roller to be rigidly attached to each other. Thus, the first end of the roller can be raised by hoisting the lifting beam, whereupon the felt can be passed from the lifting beam into its position around the rollers.
The felt changing device preferably comprises a hoisting device for raising the lifting beam while it is being attached to the first end of the first roller and for raising the lifting beam attached to the first roller. Depending on the case, the hoisting device used may consist of e.g. a beam hoist present in the factory hall, another separate hoist, hydraulic jacks, a forklift truck that can be driven to the place if necessary, and so on.
The lifting beam preferably consists of a substantially round, elongated body, which may be of a solid structure or which may consist of a gridded or latticed structure, bars or some other structure, It may also have a round shape only in its upper surface, i.e. in the portion carrying the felt.
In a preferred case, the surface of the is elongated body, at least in its upper part, comprises sliding elements, rollers, rolls, wheels or equivalent, mounted on axles transverse to the longitudinal direction of the lifting beam, carrying the belt and allowing it to be readily moved in the longitudinal direction of the lifting beam.
The felt changing device preferably comprises a supporting frame which bears the lifting beam. The supporting frame may be provided with hoist brackets by which the entire felt changing device can be moved and hoisted using suitable hoisting apparatus, such as cranes. Likewise, the supporting frame may be provided with wheels, in which case the whole felt changing device can be pushed or pulled along the floor. The lifting beam is preferably attached to the supporting frame mainly by one end only so that it is free of any supporting attachments to the supporting frame at least in its length covered by the total width of the felt. This allows a partially unwound felt roll to be pushed completely onto the lifting beam without creasing or bending the felt.
In an embodiment of the invention, the supporting frame comprises hoisting means below a fixedly mounted lifting beam, e.g. hydraulic jacks or equivalent, which can be used to adjust the vertical position of the lifting beam relative to the machine room floor below.
The fixing elements and their counter elements used preferably consist of various pins, bars, shaft stubs and tightly fitting counter elements fitted inside or outside them which have a sufficient length in the axial direction of the roller and lifting beam so that the lifting beam and the roller can be attached to each other substantially rigidly.
In the felt changing device of the invention, the felt can be moved relatively lightly in a straight condition onto the lifting beam and from the lifting beam into position around the rollers by merely pushing and pulling by hand. However, in an embodiment of the invention, the felt changing device comprises transfer means, pulling or pushing means, which can be used to move the felt. Such means may consist e.g. of catches attached to the edge of the felt and a wire rope extending from it, allowing the felt to be moved by pulling at the wire rope, manually or mechanically.
In an embodiment of the invention, the felt changing device comprises transfer elements by means of which the rollers inside the felt can be moved closer to each other and to the vicinity of the first roller. The first roller is preferably supported by a bearing bracket structure provided with sockets for the other rollers inside the felt. Thus, when the other rollers are brought close to the first roller, they can be held in place in the sockets while the felt is being passed around them.
The device and procedure of the invention for changing a felt have significant advantages as compared with prior art. Preparations for a felt change can be made in advance by bringing a felt changing device to the spot and placing the felt in it while the machine is still running. The felt remains straight and clean during the entire changing operation because it need not be spread out before installation. Neither is the felt creased or bent because it can be unwound from the roll directly in its place of use. The time and down-time required for the installation proper is reduced to a third of the corresponding time needed when prior-art techniques are used. Moreover, when installed, the felt is at once straight and clean and ready for use without any cleaning operations as are required in prior art. A further significant advantage is that a simpler and lighter structure can be used in the machine, such as a press. The press frame can be constructed without edgings and it need not be provided with heavy cantilever girders, which means a significant space saving on the driving side as well as significant savings in construction expenses.